The blade roots of turbomachine blades are exposed to high mechanical loads during operation of the turbomachine. This especially applies to the blade roots of rotor blades, via which roots the flow-induced forces which act upon the respective blade during operation, and also the centrifugal forces which act upon the respective blade, are diverted into the adjoining shaft components. In addition to mechanical loads, high thermal loads additionally occur, particularly in turbine blades.
The inverted T-root type of construction, and also the fir-tree type of construction, are blade root types of construction which are known from the prior art and which are largely common. In the blade root, which in most cases is formed in a triangular shape, at least one slot for a back-gripping fixing in an adjoining component is arranged in each case on the two free sides of the triangle. The component which adjoins the blade root in the assembly arrangement of the turbomachine has a recess which corresponds to the contour of the blade root, for positive-locking retention of the blade root. Ribs or thickenings which engage in the slots of the blade root in the assembly arrangement, are arranged in the recess of the component. The blade root of the blade, therefore, can be inserted in a positive locking manner in the recess of the component, and is fixed in the component by means of the ribs or thickenings which engage in a back-gripping manner in the slots.
The forces which act upon the blade during operation of the turbomachine, therefore, are transmitted to a significant extent to the respectively adjoining component via the surface abutment which occurs in the pairings of slot/rib or thickening. However, the slots which are arranged in the blade root, at the same time lead to a local weakening of the blade root on account of notch effect. Fatigue phenomena of the blade roots, therefore, often occur first in the region of the slots. Crack formations occur in this case. The relevant blade then has to be overhauled or exchanged. The service life of the blade, therefore, is frequently limited by the maximum continuous load bearing capability of the blade root in the region of the slots.
Indeed, it was sought to improve the continuous load bearing capability of the blade roots by means of known surface treatments, like, for example, sandblasting or shot-peening, or coating of the surfaces. By means of these surface treatments, the surfaces can indeed be hardened, so that these are loadable by higher surface loads, especially also by momentarily higher local loads. The fatigue phenomena, which are caused by low-frequency alternating or vibrating loads, which represent a significant cause for the creation of fatigue crack formations, cannot be improved, however, as a result of this.